Seismic events, high winds, or other mechanical disturbances pose the potential for major damage and even destruction of buildings. Design practices and building codes provide mitigating approaches to building design and construction that introduce some degree of lateral flexibility in buildings. This lateral flexibility allows buildings undergoing such events or disturbances to deform without being permanently damaged in any significant way from a basic structural standpoint. This deformation takes the form generally of lateral drift of the floors of the building. Lateral drift varies from floor to floor from the bottom to the top of the building. Drift generally increases from the bottom floor to the top floor such that there is relative lateral motion between consecutive floors. Lateral drift is, however, reversible. That is, when, for example, the high winds cease, such buildings will return to basically their original shape and retain their structural integrity. Floors move laterally back to their original positions one above the other.
The amount of lateral drift typical in such events depends upon the particular structural form of the building. In moment frame design, where floors are supported essentially by columns spaced throughout the building, the lateral stability of the building is dependent on the bending stiffness of the columns collectively. In such building designs, lateral floor-to-floor drifts of 2 to 3 inches are common under seismic loading. In steel braced or concrete shear wall designs, lateral stability is dependent upon various kinds of cross bracing or shear walls associated with vertical supports. In such structures under the same kind of seismic event, floor-to-floor drifts of 0.5 to 0.75 inches may be experienced.
Walls defining areas within such buildings, and particularly exterior walls enclosing the building, are commonly non load-bearing walls. Such non load-bearing walls will, for example, enclose a space between two adjacent floors, or a part of a story of the building. Walls are never anchored to both floors which define the story. Rather, walls are anchored, for example, to the lower floor and allowed to move relative to the upper floor. Such walls must accommodate relative lateral drift between floors. Lateral drift in the plane of a wall, for example, is accommodated by a slidable attachment of the wall to the upper floor such that when the floors drift relatively, the wall slides along with the lower floor. Designs to provide such slidable attachment include slotted slip tracks or nested tracks engaging the upper portions of the walls and connecting them to the upper floors. These designs provide a degree of rotational freedom of the wall relative to both the lower and upper floors as well as lateral slidability in the plane of the wall relative to the upper floor. These and similar extant connection approaches also accommodate any vertical relative movement of the floors which may occur in connection with the various kinds of building disturbing events. The accommodation of lateral drift is, however, the major concern.
Lateral drift in a direction out of the plane of a wall is accompanied by a tilting of the wall in the direction of the relative lateral drift. Rotational freedom provided by the lower and upper floor wall attachments allows a degree of tilting within limits. Lateral drift within the plane of a wall is accommodated by the wall sliding relative to the upper floor. This ability to slide derives from the slidable connection mentioned above. Any in-plane separations between adjacent co-planar walls are easily accommodated by extant devices such as flexible joints, tracks, and slotted clips. Where adjacent walls are not co-planar, for example at a corner, there is a problem in maintaining the integrity and appearance of the corner.
The problem with angled adjacent walls is most clearly understood by considering a simple right-angled building corner and by envisioning one story of a building. The walls are anchored to the floor as described above and meet at the 90 degree corner. The walls are generally connected at the corners and provided with enclosing trim or other corner treatment to seal the walls at the corner. The walls are slidably connected to the upper floor as described above. A lateral drift of the upper floor relative to the lower floor in a direction parallel to one wall will push the top of the other wall away from the corner. The other wall remains fixed to the floor and does not move away from the corner. As the wall being pushed away by the lateral drift of the top floor tilts and/or bends a generally triangular gap will occur at the corner. The apex of the triangular gap is at the lower floor level, and the gap becomes progressively wider towards the upper floor. This gaping damages the corner structure of the wall, compromising the integrity of the closure of the wall and creating an aesthetic deficit for the building. Practical means are needed to prevent such corner damage.